1. Field of the Invention
This invention relates to a film forming unit for forming a coating layer on a surface of a substrate.
2. Description of the Related Art
In the process for manufacturing semiconductor devices, for example, the photolithography process including resist coating processing for coating a resist solution on a wafer surface to form a resist layer, exposure processing for exposing to define a pattern on a wafer, developing treatment for developing the wafer having been exposed, and so on is performed with the respective processing devices to form a predetermined circuit pattern on the wafer.
In the above resist coating processing, the resist solution is discharged from a coating solution discharge nozzle toward above of the wafer. The coating solution discharge nozzle is contaminated by the resist solution and the like and thus needed to clean as necessary.
Conventionally, the coating solution discharge nozzle is cleaned with a cleaning fluid of solvent or the like such that a discharging port of the coating solution discharge nozzle is dipped into the solvent stored in a cleaning bath.
However, fine contamination cannot be perfectly removed by simply dipping as in the conventional manner. Furthermore, with recent advances in semiconductor technology, the desire to reduce a hole diameter of the aforementioned discharging port to approximately 200 μm grows. On such a minute diameter, a high effectiveness of cleaning is not expected from the conventional cleaning method as described above, with the result that minute contaminations may remain on the above discharging port.
If contaminant is adhered even slightly on the discharging port of the coating solution discharge nozzle, a direction or pressure of discharing the resist solution is varied and thus the resist solution is not coated appropriately on the wafer, resulting in a possibility of forming no coating layer having uniform thickness.
Conventionally, as shown in FIG. 21, the resist solution stored in a resist solution reservoir 213 is sent into a flow channel by a press type pump 216 such as a bellows pump, passed through a filter 217 or the like, and then supplied from the above coating solution discharge nozzle 211 onto the surface of a wafer W. In this event, the resist solution 213 for, e.g. five wafers W is stored in the bellows pump 216, and the resist solution 213 for one wafer W is pushed out from the bellows pump 216 to be supplied from the nozzle 211 onto the surface of the wafer W.
The discharge pressure of the coating solution discharge nozzle exerts an influence upon the volume of resist solution supplied onto the wafer W as it is. Hence, in order to insure uniform film-thickness, the discharge pressure for the resist solution is required to keep approximately constant.
In a conventional supply system for the resist solution, when a long time, for example, around one minute is taken for discharge, it is difficult to maintain the discharge pressure at a constant value. This produces variation in the volume of resist solution supplied to the wafer W. As a result, the uniform film-thickness of the resist layer may become worse.